Q. What is light pollution?
A. Simply put, light pollution is light that is allowed to go where it is
not wanted. Light pollution is often referred to as "skyglow" and "light
trespass". A common misconception and frequently quoted urban myth is that
the only thing that humans have created which is visible from space is the
Great Wall of China: It is in fact the light we send upwards from our
planet at night!
Satellite images of Earth show a tremendous variety of features, but one
might think that images showing parts of Earth during the hours of
darkness would be unrecognisable. The sad fact is that they are often all
too easy to recognise because of the artificial light that is poorly used
and allowed to 'leak' upwards. Major cities, towns, motorways, roads and
many other man-made features are all clearly visible from space nowadays
due to wasted light. And the problem appears to be getting worse.
Q. What causes light pollution?
A. Any exterior light source that permits light to go upwards or where it
is not needed:
Unnecessary - Lights that have no useful purpose or are lit when not
Excessive - Lights that are too numerous or simply too bright.
Badly designed - Lights that are not properly shielded or have no
shielding at all.
Badly installed - Lights that are poorly directed or situated.
Older street lights are a major cause of urban skyglow. In some instances,
lighting schemes for streets, precincts and commercial premises are simply
'over the top' and indiscriminate to no overall gain and are simply
wasteful. Illuminated signs and buildings contribute further as does
uncontrolled and badly designed and installed domestic lighting.
Q. What does light pollution affect?
A. It affects each and every one of us, not just astronomers. Light
pollution is a nuisance, it is wasteful and despoils the night time
environment and places an unnecessary strain on the planet's precious
natural resources. Light pollution makes the night sky unduly bright and
can prevent stars from being seen. Astronomy from an urban site can be
made near impossible by the encroachment of light pollution. The night sky
is a precious national and educational resource and is undoubtedly of
great special scientific interest.
Q. Is astronomy alone affected?
A. No. Excessive or bad lighting affects all living things. All exterior
lights, in particular domestic floodlights, are a common source of
nuisance if they shine into a neighbouring property. There are also
growing medical concerns as to the health effects of too much light at
night, after all, humans are not naturally nocturnal creatures. Light
pollution affects people and their interests but it also affects animals
and on a broader scale the environment. Therefore, light pollution should
be of concern to everyone.
Q. Does it affect other living things?
A. Yes. It has been observed and that in night, birds serenade a false
dawn caused by artificial light. The number of other songbirds that are
affected may be innumerable. There has been studies by RSPB (Royal Society
for the Protection of Birds) and they suggest that the decline in numbers
of many birds in recent decades may be due to the proliferation of
night-time lighting. Generally, if you can hear birds singing at night it
is because of artificial lighting - it is not normal or natural. Studies
of migratory birds have shown that they may be stimulated into premature
migration because of artificial lights. Lights can confuse creatures,
especially birds, and cause them to blunder into buildings. Deciduous
trees that are subjected to artificial light have been shown to retain
their leaves in winter on the side that is lit at night. Moths and other
insects appear to be confused by bright exterior lights. Many creatures
are nocturnal by nature and excessive night-time lighting will almost
certainly affect them in some way. These are just a few examples of how
lights can affect living things.
Q. Do security lights prevent crime?
A. This is one of the most contentious and emotive aspects of light
pollution and is worth exploring in greater detail. There is no evidence
that "security lights" deter criminals. It seems to be perceived wisdom
and belief that a light will deter or prevent a crime. But a majority of
studies in the US show no significant link between crime rates and extra
lighting. Studies in the UK have had similar results. A recent study in
the UK of lighting and crime proclaimed that additional street lights
caused a large reduction in crime statistics. However, independent
analysis of that study's findings found that the data collection and
overall analysis was flawed, invalidating the study's conclusions. It is
worth noting that the study was in fact funded by a lighting manufacturer.
Most studies of this kind indicate that the fear of crime is reduced but
the actual crime rate is not. It is worth noting that over half of all
break-ins take place in daylight, don't forget that criminals have to see
as well! Several projects and studies in US schools, colleges, and
universities have shown that vandalism actually decreases when lights are
switched off at night.
Poorly designed and installed lights are ineffective and can be dangerous
in some cases. For example, an excessively bright or poorly aimed light
may dazzle onlookers who might otherwise see and report a crime in
progress. Lighting up a secluded area may act as a courtesy light for a
would-be criminal and may even tempt criminals by making the area more
visible. For example, in UK a Dorset secondary school was never broken
into for about 20 years since its inception, being set back from the road
behind trees and unlit. Soon after sodium lights were installed all around
the building, it was broken into, not once but several times in the next
few years. As if to emphasise how little effect security lighting has,
insurance companies offer discounts for high security locks and
professionally installed alarms but they don't offer discounts for the
installation of so-called security lights.
As mentioned further up this page, a single 500 watt lamp left on all
night creates 1.25 tonnes of Carbon Dioxide annually at the power station
burning fossil fuels to keep it alight. If, for example, the cost of
the electricity is just two pence per kilowatt hour, and the light is lit,
on average, for 8 hours a day,
all year, a 500 watt lamp costs nearly £30 per year to light.
Q. Does lighting make night safer?
A. Yes, in some cases it can. Some lighting is useful for road safety, on
the street for pedestrians, so that we can see in our homes. But this does
not mean that we should light everything, everywhere, this is just
wasteful. There are some studies that show that road lighting can effect a
small decrease in accidents at known black-spots. Lighting may decrease
accidents at certain places, but excessive, poorly aimed lighting and the
glare that it causes can be counterproductive and expensive.
In some cases lighting can actually be dangerous. In France it is not
unusual to find that some streetlights are switched off around midnight,
an economy that could be used elsewhere. Clearly there is much to be
considered with regards the use of light.
Q. What does light pollution cost?
A. It is extremely difficult to state just how much light pollution costs.
While it is simple to say what may be lost or affected in some way, many
of the things affected by light pollution are simply impossible to put a
price tag on.
Q. Can light pollution be controlled?
A. Yes it can, but only by education and legislation can the trend towards
more and unnecessary lighting be halted and reversed. There is an
international trend nowadays for road lighting to be better directed.
A country that has taken a lead in controlling light pollution is
Czechoslovakia. The Czech government recently passed legislation which
prohibits the use of indiscriminate lighting with fines of up to £1000
for non-compliance. Perhaps this will trigger similar moves elsewhere; one
certainly hopes so for the sake of all those affected by excessive
Q. Can you make a difference?
Yes, you can make a difference to light pollution. Doubtless you will be
aware of environmental issues like greenhouse gases, global warming,
dwindling resources and so forth. Chances are you already take steps to
reduce the impact you have on the environment - recycling, using public
transport, insulation - there are many ways you can make a difference. Why
not go one bit further and reduce the impact that lights have on the
environment. Using low-energy bulbs, fitting lower wattage lamps,
switching lights off when they are not needed.
If you do have exterior lighting consider whether you really need it.
Again, it is necessary to repeat that there is no proof that lights
prevent crime. If you must have exterior lighting consider what brightness
it should be. Many exterior domestic lighting situations seldom require
more than a few tens of watts power at most. Can the wattage of the lamp
be reduced? Do you really need a 500 watt lamp when, say, 50 watts would
be enough? Consider the following:
Can the light be aimed so that it shines down where it is needed?
Can it be aimed so that light does not encroach onto a neighbours’
Can it be aimed so that it does not dazzle people?
Can the light be shielded to prevent light escaping to where it is not
If your own exterior lighting complies with all reasonable considerations,
what about others? If your neighbour has lighting that affects you, have
you considered raising the issue with them? They may be
unaware that they are causing a problem. If a neighbour has lights that
you consider a nuisance you can do something about it by raising the issue
with your local Authorities.
There are many ways that exterior lights can be made to have a markedly
reduced impact on the environment. And it is a win-win situation. Less
light means less light pollution. Reduced power consumption means less
fuel consumption. Reductions in consumption mean lower bills. Everyone
wins in the short and long term!